Humans as a species have been at peace for over two centuries after the earliest civilization appeared between 3000 and 4,000 years ago. According to "What Every Person Should Know About War", as many as 1 billion people may have died as a result of war.

Is violence a part of being human? Is it possible that we've evolved to be aggressive?

The answer is not easy. According to a study published in the journal Nature, Chimpanzees are prone to lethal violence in their communities.

It's possible that violence was part of the human toolkit at least as far back as our last shared Ancestor with Chimpanzees, which lived about 8 million years ago.

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Experts told Live Science that violence has been a problem for as long as humans have been alive.

David C. Geary, a cognitive scientist and evolutionary psychologist at the University of Missouri in Columbia, said in an email that violence is a driver of human history. All of humanity's early empires were built through intimidation.

"There's also evidence of aggression before recorded history, like bones with evidence of violent death, like embedded arrow points or skulls staved in," Pat Barclay told Live Science in an email. The rise of civilization is suggested by that.

Rates of violence vary vastly across cultures and communities. It suggests violence can be reduced in our species.

The eras filled with societies bent on plunder and conquest had higher levels of lethal human violence.

Modern day American culture is more violent than European ones.

The violence rates have an order of magnitude difference. Up to half of all men die violently at the hands of other men. Physical violence is very rare in other societies.

Why do people become violent?

Close up of Caucasian man's angry, clenched fist

Anyone could be capable of violence. (Image credit: Andranik Hakobyan via Getty Images)

Cultures where conflict is common are more likely to experience violence generation after generation. Gary Slutkin of the University of Illinois said that violence is transmitted as a disease.

Brad Evans, a professor of political violence at the University of Bath in the U.K., said that even people in the most progressive and peaceful communities can be violent. Ordinary, lawful persons can quickly turn into monsters once conditions change; equally, some who are most dislikeable can end up showing incredible acts of kindness. There is no formula for why someone would act in a violent way. Evans told Live Science that it's a complex problem because of that.

If the individual committing the violence is far away from their victims, it is easier to hit them with a nuke than it is to hit them with a gun.

Participants were more reluctant to shock victims if they were closer to them than if they were farther away.

The act of genocide occurs when perpetrators dehumanize or create psychological distance between themselves and those of a different race or ethnicity.

Types of violence

There may be two types of aggression in human evolution, according to a research professor at Harvard University. Conquest is when a group is determined to take the resources or land of another. The direct response to such aggression is called reactive violence.

There is room for optimism even though violence seems to be ingrained in humans.

He said that anyone is less likely to suffer violence today than in the past. Currently, we are in the most peaceful era. It's not certain that it will stay that way. Climate change will cause more scarcity, more disasters, more desperation and more reason for conflict.

It was originally published on Live Science